Windows Update can be misused to attack corporate networks through exploitation of insecurely configured enterprise implementations of Windows Server Update Services (WSUS), security researchers have claimed.
WSUS allows admins to co-ordinate software updates to servers and desktops throughout their organisations, but the Microsoft default install for WSUS is to use HTTP and not SSL-encrypted HTTPS delivery.
By exploiting this weakness, Context Information Security researchers were able to use low-privileged access rights to set up fake updates that installed automatically.
These updates could potentially download a Trojan or other malware and be used to set up admin access with a false user name and password. Any Windows computer that fetches updates from a WSUS server using a non-HTTPS URL is vulnerable.
Organisations can identify the vulnerability by checking the WSUS group policy settings, and individual machines can be scanned for the vulnerability through checking the URL, which is expected to be vulnerable if it does not have https in the URL.
Researchers from Context said that users must follow Microsoft‘s guidelines to use SSL for WSUS to protect their systems and suggested that there are further ‘defence in depth’ mitigations that can be implemented by Microsoft to offer further protection.
Black Hat joint presenter Alex Chapman said: "Using a separate signing certificate for Windows Update would increase protection and the update metadata itself could be signed by Microsoft to prevent tampering.
"Signing the tags that contain the main detail of the updates with a Microsoft certificate would avoid the necessity of setting up a trust relationship between the client and WSUS server."
